The potential use of in vivo fluorescent measurement for tissue identification has been an active field of research. In the field of oncology, Profio reported on the localization of lung tumors using tumor specific fluorescence porphyrin dies. Profio A. E. et al, Fluorescent Bronchoscopy for Localization of Carcinoma In Situ, Medical Physics. The potential application of this technology to cardiology became apparent with the discovery that porphyrin derivatives were selectively taken up by atherosclerotic plaques. Spears, J. R. et al Fluorescence of Experimental Atheromatosus Plaques with Hematoporphyrin Derivatives, J. Clin. In Vest. 71, page 395 [1938]. Problems arose because the hematoporphyrin drug had a number of adverse side effects.
It has been observed that plaque in normal tissue has autofluorescence, as observed in post-mortem arterial samples by Kittrell C. et al, Diagnosis of Fibrous Arterial Atherosclerosis Using Fluorescence, Lasers in Medical Science [1987]. Kitrell's observation was based mainly on an experimental artifact but nonetheless provided the impetus for further studies which indicated other differences in the autofluorescence spectrum that could be used for plaque identification. Anderson, P. S., Diagnosis of Arterial Atherosclerosis using Laser-induced Fluorescence, Lasers in Medical Science, 2 p. 261, [1987]; Clark, R. H. et al., Spectroscopitc Characterization of Cardiovascular Tissue., Lasers in Surgery and Medicine, 8 p. 45, [1988]; Deckelbaum, L. I. et al., In-vivo Fluorescence Spectroscopy of Normal and Atherosclerotic Arteries, SPIE V. 906 Optical Fibers in Medicine III [1988]; Leon M. B. et al, Human Arterial Surface Fluorescence; Atherosclerotic Plaque Identifiecation and Effects to Laser Atheroma Ablation, JACC, 12: 1p.94, [1988]. Among these studies included in vivo work that showed that the autofluorescence signal, even though being quite low, was sufficient for spectral discrimination.
The present invention utilized a novel approach to spectral analysis of normal structural tissue versus atherosclerotic plaque to determine a specific method of identifying atherosclerotic plaque from structurally viable tissue. The present invention further provides a means of discriminating arterial tissue surface from arterial tissue surface from which plaque has been removed. Finally, the present invention provides a base from which a more indepth identification of chemical differences can be made between atherosclerotic plaque and structural viable tissue types.